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16 March 2009 EuNPC, Bochum 1
Kaon Photoproduction Results from CLAS
D. G. Ireland
2
“Missing” Baryon Resonances
3
Resonance Hunting…
Mostly done with N scattering or photoproductionMissing resonances may decay through other channels
Total Cross-sections+ differential cross-sections+ Partial Wave Analysis + ...
0.5 1.0 1.5
Cro
ss s
ecti
on
E (GeV)
P33
N(1440)P11
N(1520)D13
N(1535)S11
(1600)P33
4
Meson Photoproduction Cross Sections
5
Evidence for new resonance?
With D13
Without D13
Mart & Benhold, Phys. Rev. C 61 012201(R) (1999)
6
Transversity Amplitudes
b1 = 1/2[(S1 + S2) + i(N - D)] p
K }} p
K }} p
K }} p
K }}
b2 = 1/2[(S1 + S2) - i(N - D)]
b3 = 1/2[(S1 - S2) - i(N + D)]
b4 = 1/2[(S1 - S2) + i(N + D)]
N, S1,S2, D: Helicity Amplitudes
7
Experimental Observables
8
p →K Reaction Kinematics
proton
zy
x
z
y
x
zy
x
p
. .c m
K
proton
K+
zzzz
yy
xxxx
CPOP
TPP
CPOP
Pd
d
cos2sincos
2coscoscos
cos2sincos
2cos10
Cross Section without target polarisationHyperon is self-analysing
9
CEBAF at Jefferson Laboratory
10
CLAS
11
Tagged Photons at CLAS
• E = E0 – E’
• Circular Polarisation: polarised electron beam, amorphous radiator
• Linear polarisation: Crystal (diamond) radiator
12
p →K Cross Section Measurements
R. Bradford et al., Phys. Rev. C 73, 035202 (2006).
13
Recoil Polarisation
proton
zy
x
z
y
x
zy
x
p
. .c m
K
proton
K+
zzzz
yy
xxxx
CPOP
TPP
CPOP
Pd
d
cos2sincos
2coscoscos
cos2sincos
2cos10
Hyperon is self-analysing
14
Recoil Polarisation (P) p→K
Guidal, Laget, VanderhaeghenGuidal, Laget, Vanderhaeghen
GENTGENT Kaon-MAIDKaon-MAID
J. McNabb J. McNabb et alet al. (CLAS) Phys. Rev. C . (CLAS) Phys. Rev. C 6969, 042201 (2004)., 042201 (2004).
15
Beam-Recoil Double Polarisation (Cx’,Cz’)
proton
zy
x
z
y
x
zy
x
p
. .c m
K
proton
K+
zzzz
yy
xxxx
CPOP
TPP
CPOP
Pd
d
cos2sincos
2coscoscos
cos2sincos
2cos10
Hyperon is self-analysing
16
Polarisation
2 2 2x zR P C C
→ fully polarised
R. Bradford et al., Phys. Rev. C 75, 035205 (2007).
17
Photon Beam Asymmetry ()
proton
zy
x
z
y
x
zy
x
p
. .c m
K
proton
K+
zzzz
yy
xxxx
CPOP
TPP
CPOP
Pd
d
cos2sincos
2coscoscos
cos2sincos
2cos10
18
Linear Polarisation analysis
Photon Linear Polarisation Particle ID
Thesis work of Craig Paterson (Glasgow)
19
p →K Photon Beam Asymmetry
20
p →K Photon Beam Asymmetry
PREL
IMIN
ARY
21
p →K Photon Beam Asymmetry
PREL
IMIN
ARY
22
Beam-Recoil Double Polarisation (x,Oz)
proton
zy
x
z
y
x
zy
x
p
. .c m
K
proton
K+
zzzz
yy
xxxx
CPOP
TPP
CPOP
Pd
d
cos2sincos
2coscoscos
cos2sincos
2cos10
23
p →K Extracting Ox and Oz
24
p →K Beam-Recoil Ox and Oz
O x
PREL
IMIN
ARY
O z
PREL
IMIN
ARY
25
Experimental Observables
26
Outlook – Deuterium Target
• Data taking completed
• Currently being analysed
• Data on quasifree neutron and proton
• Circular and Linear Polarisation
27
Outlook – FROzen Spin Target (FROST)
Target can be longitudinally or transversely polarised
• “Complete” measurement possible• First part of run complete• Undergoing calibration• Second period to run soon…
28
Conclusions
Kaon Photoproduction results from CLAS:
• Published results: , P, Cx, Cz
• Preliminary results: , T, Ox, Oz
In the near future:
• Same set of results for 2H target (quasifree neutron and proton)
• “Complete” results (FROST)
Next few years:
• Complete set on 2H and p (HDIce)
29
Backup Slides…
30
Resonances in Quark Models
31
Kaon Photoproduction
32
Contributing Processes
+ channel coupling…
33
Helicity Amplitudes
N No overall helicity flip = |–p |
p
K }}S1 Single helicity flip
p
K }}S2 Single helicity flip
p
K }}D Double helicity flip
p
K }}
34
Cross Section Measurements
R. Bradford et al., Phys. Rev. C 73, 035202 (2006).
35
Cross Section Measurements
R. Bradford et al., Phys. Rev. C 73, 035202 (2006).
36
Cross Section Measurements
R. Bradford et al., Phys. Rev. C 73, 035202 (2006).
37
Beam-Recoil Double Polarisation Cz
R. Bradford et al., Phys. Rev. C 75, 035205 (2007).
Saclay, Argonne, PittsburghSaclay, Argonne, Pittsburgh
Bonn, Giessen, GatchinaBonn, Giessen, GatchinaKaon-MAIDKaon-MAID
Regge+ResonanceRegge+Resonance GENTGENT
Shklyar Shklyar Lenske Lenske MoselMosel
38
Beam-Recoil Double Polarisation Cx
GENTGENT
Saclay, Argonne, PittsburghSaclay, Argonne, Pittsburgh
Bonn, Giessen, GatchinaBonn, Giessen, Gatchina
Kaon-MAIDKaon-MAID
Regge+ResonanceRegge+Resonance
Shklyar Lenske Shklyar Lenske MoselMosel
R. Bradford et al., Phys. Rev. C 75, 035205 (2007).
39
Photon Beam Asymmetry
40
Photon Beam Asymmetry
PREL
IMIN
ARY
41
Photon Beam Asymmetry
PREL
IMIN
ARY
42
Recoil - Comparison
g8b
Prev CLAS
GRAAL
~Factor of 4 increase in statistics from best previous measurements
PREL
IMIN
ARY